Spinal cannulas are used for puncturing the spinal cavity, wherein the liquor backflow must be controlled so that the correct positioning of the needle tip in the subarachnoid cavity can be controlled. The difficulty hereby is that the waterwhite and colourless liquor cannot easily be optically recognised in the needle hub.
From U.S. Pat. No. 6,656,161, a spinal cannula having a transparent area at the needle hub is known, at which a magnifying lens is formed so that the liquor backflow can be recognised.
From EP 682 954, a spinal cannula having a transparent grip part is known, in which a liquor control chamber tapering toward the needle end is formed, which has a substantially rectangular cross-sectional shape with flat wall areas extending toward each other pair-wise in a wedge-shaped manner. In this embodiment, it is to be ensured that the liquor backflow inside the liquor control chamber is well recognisable without interfering reflexes and light refraction.